ages pipes -- aging pipes. one of the main gas suppliers here in the state of massachusetts says in the past three years they've replaced approximately 300 miles of aging pipe here in massachusetts. jon? jon: yeah, and hats off to the professor for, you know, showing some real world work to his students. i mean, they seem to do some good stuff there. >> reporter: yeah, fascinating. jon: molly line, thank you. jenna: well, the nation's recovery is slowly recovering from the recession, at least that's what we hear. only three major american cities are really bouncing back so far. harris has more on this and who are the lucky three, harris? [laughter] >> reporter: yeah, exactly, jenna. the brookings institution, a washington-based research group, looked at unemployment levels among other things in our nation's leading cities. let's start though, jenna, with the good news of the story, because if you're in knoxville, tennessee, if you're in dallas, texas or pittsburgh, pa, life may be feeling less desperate.